In permanent magnet synchronous machines it is common to use laminated rotor structures, i.e. disk rotors, wherein the actual body of the rotor around the shaft is made from a large number of round and thin ferromagnetic metal disks that are identical in shape, disposed perpendicularly relative to the shaft and packed into a tight assembly. The permanent magnets are then provided to the body of the rotor, either to the surface or embedded deeper as rods extending from one end of the cylindrical rotor to the other.
In the invention, the permanent magnets are disposed inside the rotor body in a ring-type V-shape configuration known per se, i.e. the first ends of the permanent magnets are close to the surface of the rotor and the second ends are closer to the central axis but disposed at an angle to the radial direction. This way, every second magnet is inclined in one direction and every second in the other direction relative to the radial direction. This type of structure has been disclosed in publication JP 2006050821. The purpose of said structure has been to minimize the leakage flux and at the same time to achieve sufficient rigidity of the rotor when using permanent magnets that are embedded in the rotor.
Another structure representing the prior art has been disclosed in patent U.S. Pat. No. 4,445,062. It features permanent magnet rods embedded in the rotor, in radial grooves on the surface thereof, in such a way that the poles of the permanent magnets are disposed one after the other in the circumferential direction. The bottom of a groove is so dimensioned or shaped relative to the permanent magnet as to form on the bottom of the groove a gap that can act as a cooling air channel that extends axially through the rotor. The purpose of the structure is simply and securely to fix the magnets in place in the rotor. The publication does not discuss minimization of the leakage flux of the magnets.
The ferromagnetic disk pack constitutes a good body for the rotor around the magnets, but heating of the rotor and particularly of the magnets causes problems specifically in large machines. Another problem is the leakage flux of the rotor and the armature reaction, i.e. the magnetic flux tends to move sideways on the rotor pole, which is not a desirable phenomenon.